/**
	Implements a declarative framework for building web interfaces.

	This module contains the sister funtionality to the $(D vibe.web.rest)
	module. While the REST interface generator is meant for stateless
	machine-to-machine communication, this module aims at implementing
	user facing web services. Apart from that, both systems use the same
	declarative approach.

	See $(D registerWebInterface) for an overview of how the system works.

	Copyright: © 2013-2016 RejectedSoftware e.K.
	License: Subject to the terms of the MIT license, as written in the included LICENSE.txt file.
	Authors: Sönke Ludwig
*/
module vibe.web.web;

public import vibe.internal.meta.funcattr : PrivateAccessProxy, before, after;
public import vibe.web.common;
public import vibe.web.i18n;
public import vibe.web.validation;

import vibe.core.core;
import vibe.inet.url;
import vibe.http.common;
import vibe.http.router;
import vibe.http.server;
import vibe.http.websockets;
import vibe.web.auth : AuthInfo, handleAuthentication, handleAuthorization, isAuthenticated;

import std.encoding : sanitize;

/*
	TODO:
		- conversion errors of path place holder parameters should result in 404
		- support format patterns for redirect()
*/


/**
	Registers a HTTP/web interface based on a class instance.

	Each public method of the given class instance will be mapped to a HTTP
	route. Property methods are mapped to GET/PUT and all other methods are
	mapped according to their prefix verb. If the method has no known prefix,
	POST is used. The rest of the name is mapped to the path of the route
	according to the given `method_style`. Note that the prefix word must be
	all-lowercase and is delimited by either an upper case character, a
	non-alphabetic character, or the end of the string.

	The following table lists the mappings from prefix verb to HTTP verb:

	$(TABLE
		$(TR $(TH HTTP method) $(TH Recognized prefixes))
		$(TR $(TD GET)	  $(TD get, query))
		$(TR $(TD PUT)    $(TD set, put))
		$(TR $(TD POST)   $(TD add, create, post))
		$(TR $(TD DELETE) $(TD remove, erase, delete))
		$(TR $(TD PATCH)  $(TD update, patch))
	)

	Method parameters will be sourced from either the query string
	or form data of the request, or, if the parameter name has an underscore
	prefixed, from the $(D vibe.http.server.HTTPServerRequest.params) map.

	The latter can be used to inject custom data in various ways. Examples of
	this are placeholders specified in a `@path` annotation, values computed
	by a `@before` annotation, error information generated by the
	`@errorDisplay` annotation, or data injected manually in a HTTP method
	handler that processed the request prior to passing it to the generated
	web interface handler routes.

	Methods that return a $(D class) or $(D interface) instance, instead of
	being mapped to a single HTTP route, will be mapped recursively by
	iterating the public routes of the returned instance. This way, complex
	path hierarchies can be mapped to class hierarchies.

	Parameter_conversion_rules:
		For mapping method parameters without a prefixed underscore to
		query/form fields, the following rules are applied:

		$(UL
			$(LI A dynamic array of values is mapped to
				`<parameter_name>_<index>`, where `index`
				denotes the zero based index of the array entry. Any missing
				indexes will be left as their `init` value. Arrays can also be
				passed without indexes using the name `<parameter_name>_`. They
				will be added in the order they appear in the form data or
				query. Mixed styles can also be used, non-indexed elements will
				be used to fill in missing indexes, or appended if no missing
				index exists. Duplicate indexes are ignored)
			$(LI A static array of values is mapped identically to dynamic
				arrays, except that all elements must be present in the query
				or form data, and indexes or non-indexed data beyond the size
				of the array is ignored.)
			$(LI $(D Nullable!T) typed parameters, as well as parameters with
				default values, are optional parameters and are allowed to be
				missing in the set of form fields. All other parameter types
				require the corresponding field to be present and will result
				in a runtime error otherwise.)
			$(LI $(D struct) type parameters that don't define a $(D fromString)
				or a $(D fromStringValidate) method will be mapped to one
				form field per struct member with a scheme similar to how
				arrays are treated: `<parameter_name>_<member_name>`)
			$(LI Boolean parameters will be set to $(D true) if a form field of
				the corresponding name is present and to $(D false) otherwise.
				This is compatible to how check boxes in HTML forms work.)
			$(LI All other types of parameters will be converted from a string
				by using the first available means of the following:
				a static $(D fromStringValidate) method, a static $(D fromString)
				method, using $(D std.conv.to!T).)
			$(LI Any of these rules can be applied recursively, so that it is
				possible to nest arrays and structs appropriately. Note that
				non-indexed arrays used recursively will be ignored because of
				the nature of that mechanism.)
		)

	Special_parameters:
		$(UL
			$(LI A parameter named $(D __error) will be populated automatically
				with error information, when an $(D @errorDisplay) attribute
				is in use.)
			$(LI An $(D InputStream) typed parameter will receive the request
				body as an input stream. Note that this stream may be already
				emptied if the request was subject to certain body parsing
				options. See $(D vibe.http.server.HTTPServerOption).)
			$(LI Parameters of types $(D vibe.http.server.HTTPServerRequest),
				$(D vibe.http.server.HTTPServerResponse),
				$(D vibe.http.common.HTTPRequest) or
				$(D vibe.http.common.HTTPResponse) will receive the
				request/response objects of the invoking request.)
			$(LI If a parameter of the type `WebSocket` is found, the route
				is registered as a web socket endpoint. It will automatically
				upgrade the connection and pass the resulting WebSocket to
				the connection.)
		)


	Supported_attributes:
		The following attributes are supported for annotating methods of the
		registered class:

		$(D @before), $(D @after), $(D @errorDisplay),
		$(D @vibe.web.common.method), $(D @vibe.web.common.path),
		$(D @vibe.web.common.contentType)

		The `@path` attribute can also be applied to the class itself, in which
		case it will be used as an additional prefix to the one in
		`WebInterfaceSettings.urlPrefix`.

		The $(D @nestedNameStyle) attribute can be applied only to the class
		itself. Applying it to a method is not supported at this time.

	Supported return types:
		$(UL
			$(LI $(D vibe.data.json.Json))
			$(LI $(D const(char)[]))
			$(LI $(D void))
			$(LI $(D const(ubyte)[]))
			$(LI $(D vibe.core.stream.InputStream))
		)

	Params:
		router = The HTTP router to register to
		instance = Class instance to use for the web interface mapping
		settings = Optional parameter to customize the mapping process
*/
URLRouter registerWebInterface(C : Object, MethodStyle method_style = MethodStyle.lowerUnderscored)(URLRouter router, C instance, WebInterfaceSettings settings = null)
{
	import std.algorithm : endsWith;
	import std.traits;
	import vibe.internal.meta.uda : findFirstUDA;

	if (!settings) settings = new WebInterfaceSettings;

	string url_prefix = settings.urlPrefix;
	enum cls_path = findFirstUDA!(PathAttribute, C);
	static if (cls_path.found) {
		url_prefix = concatURL(url_prefix, cls_path.value, true);
	}

	foreach (M; __traits(allMembers, C)) {
		/*static if (isInstanceOf!(SessionVar, __traits(getMember, instance, M))) {
			__traits(getMember, instance, M).m_getContext = toDelegate({ return s_requestContext; });
		}*/
		static if (!is(typeof(__traits(getMember, Object, M)))) { // exclude Object's default methods and field
			foreach (overload; MemberFunctionsTuple!(C, M)) {
				alias RT = ReturnType!overload;
				enum minfo = extractHTTPMethodAndName!(overload, true)();
				enum url = minfo.hadPathUDA ? minfo.url : adjustMethodStyle(minfo.url, method_style);

				static if (findFirstUDA!(NoRouteAttribute, overload).found) {
					import vibe.core.log : logDebug;
					logDebug("Method %s.%s annotated with @noRoute - not generating a route entry.", C.stringof, M);
				} else static if (is(RT == class) || is(RT == interface)) {
					// nested API
					static assert(
						ParameterTypeTuple!overload.length == 0,
						"Instances may only be returned from parameter-less functions ("~M~")!"
					);
					auto subsettings = settings.dup;
					subsettings.urlPrefix = concatURL(url_prefix, url, true);
					registerWebInterface!RT(router, __traits(getMember, instance, M)(), subsettings);
				} else {
					auto fullurl = concatURL(url_prefix, url);
					router.match(minfo.method, fullurl, (HTTPServerRequest req, HTTPServerResponse res) @trusted {
						handleRequest!(M, overload)(req, res, instance, settings);
					});
					if (settings.ignoreTrailingSlash && !fullurl.endsWith("*") && fullurl != "/") {
						auto m = fullurl.endsWith("/") ? fullurl[0 .. $-1] : fullurl ~ "/";
						router.match(minfo.method, m, delegate void (HTTPServerRequest req, HTTPServerResponse res) @safe {
							static if (minfo.method == HTTPMethod.GET) {
								URL redurl = req.fullURL;
								auto redpath = redurl.path;
								redpath.endsWithSlash = !redpath.endsWithSlash;
								redurl.path = redpath;
								res.redirect(redurl);
							} else {
								() @trusted { handleRequest!(M, overload)(req, res, instance, settings); } ();
							}
						});
					}
				}
			}
		}
	}
	return router;
}


/**
	Gives an overview of the basic features. For more advanced use, see the
	example in the "examples/web/" directory.
*/
unittest {
	import vibe.http.router;
	import vibe.http.server;
	import vibe.web.web;

	class WebService {
		private {
			SessionVar!(string, "login_user") m_loginUser;
		}

		@path("/")
		void getIndex(string _error = null)
		{
			header("Access-Control-Allow-Origin", "Access-Control-Allow-Origin: *");
			//render!("index.dt", _error);
		}

		// automatically mapped to: POST /login
		@errorDisplay!getIndex
		void postLogin(string username, string password)
		{
			enforceHTTP(username.length > 0, HTTPStatus.forbidden,
				"User name must not be empty.");
			enforceHTTP(password == "secret", HTTPStatus.forbidden,
				"Invalid password.");
			m_loginUser = username;
			redirect("/profile");
		}

		// automatically mapped to: POST /logout
		void postLogout()
		{
			terminateSession();
			status(201);
			redirect("/");
		}

		// automatically mapped to: GET /profile
		void getProfile()
		{
			enforceHTTP(m_loginUser.length > 0, HTTPStatus.forbidden,
				"Must be logged in to access the profile.");
			//render!("profile.dt")
		}
	}

	void run()
	{
		auto router = new URLRouter;
		router.registerWebInterface(new WebService);

		auto settings = new HTTPServerSettings;
		settings.port = 8080;
		listenHTTP(settings, router);
	}
}


/**
	Renders a Diet template file to the current HTTP response.

	This function is equivalent to `vibe.http.server.render`, but implicitly
	writes the result to the response object of the currently processed
	request.

	Note that this may only be called from a function/method
	registered using `registerWebInterface`.

	In addition to the vanilla `render` function, this one also makes additional
	functionality available within the template:

	$(UL
		$(LI The `req` variable that holds the current request object)
		$(LI If the `@translationContext` attribute us used, enables the
		     built-in i18n support of Diet templates)
	)
*/
template render(string diet_file, ALIASES...) {
	void render(string MODULE = __MODULE__, string FUNCTION = __FUNCTION__)()
	{
		import vibe.web.i18n;
		import vibe.internal.meta.uda : findFirstUDA;
		mixin("static import "~MODULE~";");

		alias PARENT = typeof(__traits(parent, mixin(FUNCTION)).init);
		enum FUNCTRANS = findFirstUDA!(TranslationContextAttribute, mixin(FUNCTION));
		enum PARENTTRANS = findFirstUDA!(TranslationContextAttribute, PARENT);
		static if (FUNCTRANS.found) alias TranslateContext = FUNCTRANS.value.Context;
		else static if (PARENTTRANS.found) alias TranslateContext = PARENTTRANS.value.Context;

		assert(s_requestContext.req !is null, "render() used outside of a web interface request!");
		auto req = s_requestContext.req;

		struct TranslateCTX(string lang)
		{
			version (Have_diet_ng) {
				import diet.traits : dietTraits;
				@dietTraits static struct diet_translate__ {
					static string translate(string key, string context=null) { return tr!(TranslateContext, lang)(key, context); }
				}
			} else static string diet_translate__(string key,string context=null) { return tr!(TranslateContext, lang)(key, context); }

			void render()
			{
				vibe.http.server.render!(diet_file, req, ALIASES, diet_translate__)(s_requestContext.res);
			}
		}

		static if (is(TranslateContext) && languageSeq!TranslateContext.length) {
			switch (s_requestContext.language) {
				default:
				mixin({
					string ret;
					foreach (lang; TranslateContext.languages)
						ret ~= "case `" ~ lang ~ "`: {
							TranslateCTX!`" ~ lang ~ "` renderctx;
							renderctx.render();
							return;
							}";
					return ret;
				}());
			}
		} else {
			vibe.http.server.render!(diet_file, req, ALIASES)(s_requestContext.res);
		}
	}
}


/**
	Redirects to the given URL.

	The URL may either be a full URL, including the protocol and server
	portion, or it may be the local part of the URI (the path and an
	optional query string). Finally, it may also be a relative path that is
	combined with the path of the current request to yield an absolute
	path.

	Note that this may only be called from a function/method
	registered using registerWebInterface.
*/
void redirect(string url, int status = HTTPStatus.found)
@safe {
	import std.algorithm : canFind, endsWith, startsWith;

	auto ctx = getRequestContext();
	URL fullurl;
	if (url.startsWith("/")) {
		fullurl = ctx.req.fullURL;
		fullurl.localURI = url;
	} else if (url.canFind(":")) { // TODO: better URL recognition
		fullurl = URL(url);
	} else  if (ctx.req.fullURL.path.endsWithSlash) {
		fullurl = ctx.req.fullURL;
		fullurl.localURI = fullurl.path.toString() ~ url;
	} else {
		fullurl = ctx.req.fullURL.parentURL;
		assert(fullurl.localURI.endsWith("/"), "Parent URL not ending in a slash?!");
		fullurl.localURI = fullurl.localURI ~ url;
	}
	ctx.res.redirect(fullurl, status);
}

/// ditto
void redirect(URL url, int status = HTTPStatus.found)
@safe {
	redirect(url.toString, status);
}

///
@safe unittest {
	import vibe.data.json : Json;

	class WebService {
		// POST /item
		void postItem() {
			redirect("/item/1");
		}
	}

	void run()
	{
		auto router = new URLRouter;
		router.registerWebInterface(new WebService);

		auto settings = new HTTPServerSettings;
		settings.port = 8080;
		listenHTTP(settings, router);
	}
}

/**
	Sets a response header.

	Params:
		name = name of the header to set
		value = value of the header to set

	Note that this may only be called from a function/method
	registered using registerWebInterface.
*/
void header(string name, string value)
@safe {
	getRequestContext().res.headers[name] = value;
}

///
@safe unittest {
	import vibe.data.json : Json;

	class WebService {
		// POST /item
		Json postItem() {
			header("X-RateLimit-Remaining", "59");
			return Json(["id": Json(100)]);
		}
	}

	void run()
	{
		auto router = new URLRouter;
		router.registerWebInterface(new WebService);

		auto settings = new HTTPServerSettings;
		settings.port = 8080;
		listenHTTP(settings, router);
	}
}

/**
	Sets the response status code.

	Params:
		statusCode = the HTTPStatus code to send to the client

	Note that this may only be called from a function/method
	registered using registerWebInterface.
*/
void status(int statusCode) @safe
in
{
	assert(100 <= statusCode && statusCode < 600);
}
body
{
	getRequestContext().res.statusCode = statusCode;
}

///
@safe unittest {
	import vibe.data.json : Json;

	class WebService {
		// POST /item
		Json postItem() {
			status(HTTPStatus.created);
			return Json(["id": Json(100)]);
		}
	}

	void run()
	{
		auto router = new URLRouter;
		router.registerWebInterface(new WebService);

		auto settings = new HTTPServerSettings;
		settings.port = 8080;
		listenHTTP(settings, router);
	}
}

/**
	Returns the agreed upon language.

	Note that this may only be called from a function/method
	registered using registerWebInterface.
*/
@property string language() @safe
{
	return getRequestContext().language;
}

/**
	Returns the current request.

	Note that this may only be called from a function/method
	registered using registerWebInterface.
*/
@property HTTPServerRequest request() @safe
{
	return getRequestContext().req;
}

///
@safe unittest {
	void requireAuthenticated()
	{
		auto authorization = "Authorization" in request.headers;

		enforceHTTP(authorization !is null, HTTPStatus.forbidden);
		enforceHTTP(*authorization == "secret", HTTPStatus.forbidden);
	}

	class WebService {
		void getPage()
		{
			requireAuthenticated();
		}
	}

	void run()
	{
		auto router = new URLRouter;
		router.registerWebInterface(new WebService);

		auto settings = new HTTPServerSettings;
		settings.port = 8080;
		listenHTTP(settings, router);
	}
}

/**
	Returns the current response.

	Note that this may only be called from a function/method
	registered using registerWebInterface.
*/
@property HTTPServerResponse response() @safe
{
	return getRequestContext().res;
}

///
@safe unittest {
	void logIn()
	{
		auto session = response.startSession();
		session.set("token", "secret");
	}

	class WebService {
		void postLogin(string username, string password)
		{
			if (username == "foo" && password == "bar") {
				logIn();
			}
		}
	}

	void run()
	{
		auto router = new URLRouter;
		router.registerWebInterface(new WebService);

		auto settings = new HTTPServerSettings;
		settings.port = 8080;
		listenHTTP(settings, router);
	}
}

/**
	Terminates the currently active session (if any).

	Note that this may only be called from a function/method
	registered using registerWebInterface.
*/
void terminateSession()
@safe {
	auto ctx = getRequestContext();
	if (ctx.req.session) {
		ctx.res.terminateSession();
		ctx.req.session = Session.init;
	}
}

///
@safe unittest {
	class WebService {
		// automatically mapped to: POST /logout
		void postLogout()
		{
			terminateSession();
			201.status;
			redirect("/");
		}
	}

	void run()
	{
		auto router = new URLRouter;
		router.registerWebInterface(new WebService);

		auto settings = new HTTPServerSettings;
		settings.port = 8080;
		listenHTTP(settings, router);
	}
}

/**
	Translates text based on the language of the current web request.

	The first overload performs a direct translation of the given translation
	key/text. The second overload can select from a set of plural forms
	based on the given integer value (msgid_plural).

	Params:
		text = The translation key
		context = Optional context/namespace identifier (msgctxt)
		plural_text = Plural form of the translation key
		count = The quantity used to select the proper plural form of a translation

	See_also: $(D vibe.web.i18n.translationContext)
*/
string trWeb(string text, string context = null)
@safe {
	return getRequestContext().tr(text, context);
}

/// ditto
string trWeb(string text, string plural_text, int count, string context = null)
@safe {
	return getRequestContext().tr_plural(text, plural_text, count, context);
}

///
@safe unittest {
	struct TRC {
		import std.typetuple;
		alias languages = TypeTuple!("en_US", "de_DE", "fr_FR");
		//mixin translationModule!"test";
	}

	@translationContext!TRC
	class WebService {
		void index(HTTPServerResponse res)
		{
			res.writeBody(trWeb("This text will be translated!"));
		}
	}
}


/**
	Attribute to customize how errors/exceptions are displayed.

	The first template parameter takes a function that maps an exception and an
	optional field name to a single error type. The result of this function
	will then be passed as the $(D _error) parameter to the method referenced
	by the second template parameter.

	Supported types for the $(D _error) parameter are $(D bool), $(D string),
	$(D Exception), or a user defined $(D struct). The $(D field) member, if
	present, will be set to null if the exception was thrown after the field
	validation has finished.
*/
@property errorDisplay(alias DISPLAY_METHOD)()
{
	return ErrorDisplayAttribute!DISPLAY_METHOD.init;
}

/// Shows the basic error message display.
unittest {
	void getForm(string _error = null)
	{
		//render!("form.dt", _error);
	}

	@errorDisplay!getForm
	void postForm(string name)
	{
		if (name.length == 0)
			throw new Exception("Name must not be empty");
		redirect("/");
	}
}

/// Advanced error display including the offending form field.
unittest {
	struct FormError {
		// receives the original error message
		string error;
		// receives the name of the field that caused the error, if applicable
		string field;
	}

	void getForm(FormError _error = FormError.init)
	{
		//render!("form.dt", _error);
	}

	// throws an error if the submitted form value is not a valid integer
	@errorDisplay!getForm
	void postForm(int ingeter)
	{
		redirect("/");
	}
}

/** Determines how nested D fields/array entries are mapped to form field
 * names. Note that this attribute only works if applied to the class.
*/
NestedNameStyleAttribute nestedNameStyle(NestedNameStyle style)
{
	import vibe.internal.meta.uda : onlyAsUda;
	if (!__ctfe) assert(false, onlyAsUda!__FUNCTION__);
	return NestedNameStyleAttribute(style);
}

///
unittest {
	struct Items {
		int[] entries;
	}

	@nestedNameStyle(NestedNameStyle.d)
	class MyService {
		// expects fields in D native style:
		// "items.entries[0]", "items.entries[1]", "items.entries[]", ...
		void postItems(Items items)
		{

		}
	}
}


/**
	Encapsulates settings used to customize the generated web interface.
*/
class WebInterfaceSettings {
	string urlPrefix = "/";
	bool ignoreTrailingSlash = true;

	@property WebInterfaceSettings dup() const @safe {
		auto ret = new WebInterfaceSettings;
		ret.urlPrefix = this.urlPrefix;
		ret.ignoreTrailingSlash = this.ignoreTrailingSlash;
		return ret;
	}
}


/**
	Maps a web interface member variable to a session field.

	Setting a SessionVar variable will implicitly start a session, if none
	has been started yet. The content of the variable will be stored in
	the session store and is automatically serialized and deserialized.

	Note that variables of type SessionVar must only be used from within
	handler functions of a class that was registered using
	$(D registerWebInterface). Also note that two different session
	variables with the same $(D name) parameter will access the same
	underlying data.
*/
struct SessionVar(T, string name) {
@safe:

	private {
		T m_initValue;
	}

	/** Initializes a session var with a constant value.
	*/
	this(T init_val) { m_initValue = init_val; }
	///
	unittest {
		class MyService {
			SessionVar!(int, "someInt") m_someInt = 42;

			void index() {
				assert(m_someInt == 42);
			}
		}
	}

	/** Accesses the current value of the session variable.

		Any access will automatically start a new session and set the
		initializer value, if necessary.
	*/
	@property const(T) value()
	{
		auto ctx = getRequestContext();
		if (!ctx.req.session) ctx.req.session = ctx.res.startSession();

		if (ctx.req.session.isKeySet(name))
			return ctx.req.session.get!T(name);

		ctx.req.session.set!T(name, m_initValue);
		return m_initValue;
	}
	/// ditto
	@property void value(T new_value)
	{
		auto ctx = getRequestContext();
		if (!ctx.req.session) ctx.req.session = ctx.res.startSession();
		ctx.req.session.set(name, new_value);
	}

	void opAssign(T new_value) { this.value = new_value; }

	alias value this;
}

private struct ErrorDisplayAttribute(alias DISPLAY_METHOD) {
	import std.traits : ParameterTypeTuple, ParameterIdentifierTuple;

	alias displayMethod = DISPLAY_METHOD;
	enum displayMethodName = __traits(identifier, DISPLAY_METHOD);

	private template GetErrorParamType(size_t idx) {
		static if (idx >= ParameterIdentifierTuple!DISPLAY_METHOD.length)
			static assert(false, "Error display method "~displayMethodName~" is missing the _error parameter.");
		else static if (ParameterIdentifierTuple!DISPLAY_METHOD[idx] == "_error")
			alias GetErrorParamType = ParameterTypeTuple!DISPLAY_METHOD[idx];
		else alias GetErrorParamType = GetErrorParamType!(idx+1);
	}

	alias ErrorParamType = GetErrorParamType!0;

	ErrorParamType getError(Exception ex, string field)
	{
		static if (is(ErrorParamType == bool)) return true;
		else static if (is(ErrorParamType == string)) return ex.msg;
		else static if (is(ErrorParamType == Exception)) return ex;
		else static if (is(typeof(ErrorParamType(ex, field)))) return ErrorParamType(ex, field);
		else static if (is(typeof(ErrorParamType(ex.msg, field)))) return ErrorParamType(ex.msg, field);
		else static if (is(typeof(ErrorParamType(ex.msg)))) return ErrorParamType(ex.msg);
		else static assert(false, "Error parameter type %s does not have the required constructor.");
	}
}

private struct NestedNameStyleAttribute { NestedNameStyle value; }


private {
	TaskLocal!RequestContext s_requestContext;
}

private struct RequestContext {
	HTTPServerRequest req;
	HTTPServerResponse res;
	string language;
	string function(string, string) @safe tr;
	string function(string, string, int, string) @safe tr_plural;
}

private RequestContext getRequestContext()
@trusted nothrow {
	assert(s_requestContext.req !is null, "Request context used outside of a web interface request!");
	return s_requestContext;
}

private void handleRequest(string M, alias overload, C, ERROR...)(HTTPServerRequest req, HTTPServerResponse res, C instance, WebInterfaceSettings settings, ERROR error)
	if (ERROR.length <= 1)
{
	import std.algorithm : countUntil, startsWith;
	import std.traits;
	import std.typetuple : Filter, staticIndexOf;
	import vibe.core.stream;
	import vibe.data.json;
	import vibe.internal.meta.funcattr;
	import vibe.internal.meta.uda : findFirstUDA;

	alias RET = ReturnType!overload;
	alias PARAMS = ParameterTypeTuple!overload;
	alias default_values = ParameterDefaultValueTuple!overload;
	alias AuthInfoType = AuthInfo!C;
	enum param_names = [ParameterIdentifierTuple!overload];
	enum erruda = findFirstUDA!(ErrorDisplayAttribute, overload);

	static if (findFirstUDA!(NestedNameStyleAttribute, C).found)
		enum nested_style = findFirstUDA!(NestedNameStyleAttribute, C).value.value;
	else enum nested_style = NestedNameStyle.underscore;

	s_requestContext = createRequestContext!overload(req, res);
	enum hasAuth = isAuthenticated!(C, overload);

	static if (hasAuth) {
		auto auth_info = handleAuthentication!overload(instance, req, res);
		if (res.headerWritten) return;
	}

	// collect all parameter values
	PARAMS params = void; // FIXME: in case of errors, destructors could be called on uninitialized variables!
	foreach (i, PT; PARAMS) {
		bool got_error = false;
		ParamError err;
		err.field = param_names[i];
		try {
			static if (hasAuth && is(PT == AuthInfoType)) {
				params[i] = auth_info;
			} else static if (IsAttributedParameter!(overload, param_names[i])) {
				params[i].setVoid(computeAttributedParameterCtx!(overload, param_names[i])(instance, req, res));
				if (res.headerWritten) return;
			}
			else static if (param_names[i] == "_error") {
				static if (ERROR.length == 1)
					params[i].setVoid(error[0]);
				else static if (!is(default_values[i] == void))
					params[i].setVoid(default_values[i]);
				else
					params[i] = typeof(params[i]).init;
			}
			else static if (is(PT == InputStream)) params[i] = req.bodyReader;
			else static if (is(PT == HTTPServerRequest) || is(PT == HTTPRequest)) params[i] = req;
			else static if (is(PT == HTTPServerResponse) || is(PT == HTTPResponse)) params[i] = res;
			else static if (is(PT == WebSocket)) {} // handled below
			else static if (param_names[i].startsWith("_")) {
				if (auto pv = param_names[i][1 .. $] in req.params) {
					got_error = !webConvTo(*pv, params[i], err);
					// treat errors in route parameters as non-match
					// FIXME: verify that the parameter is actually a route parameter!
					if (got_error) return;
				} else static if (!is(default_values[i] == void)) params[i].setVoid(default_values[i]);
				else static if (!isNullable!PT) enforceHTTP(false, HTTPStatus.badRequest, "Missing request parameter for "~param_names[i]);
			} else static if (is(PT == bool)) {
				params[i] = param_names[i] in req.form || param_names[i] in req.query;
			} else {
				enum has_default = !is(default_values[i] == void);
				ParamResult pres = readFormParamRec(req, params[i], param_names[i], !has_default, nested_style, err);
				static if (has_default) {
					if (pres == ParamResult.skipped)
						params[i].setVoid(default_values[i]);
				} else assert(pres != ParamResult.skipped);

				if (pres == ParamResult.error)
					got_error = true;
			}
		} catch (HTTPStatusException ex) {
			throw ex;
		} catch (Exception ex) {
			import vibe.core.log : logDebug;
			got_error = true;
			err.text = ex.msg;
			debug logDebug("Error handling field '%s': %s", param_names[i], ex.toString().sanitize);
		}

		if (got_error) {
			static if (erruda.found && ERROR.length == 0) {
				auto errnfo = erruda.value.getError(new Exception(err.text), err.field);
				handleRequest!(erruda.value.displayMethodName, erruda.value.displayMethod)(req, res, instance, settings, errnfo);
				return;
			} else {
				throw new HTTPStatusException(HTTPStatus.badRequest, "Error handling field '"~err.field~"': "~err.text);
			}
		}
	}

	// validate all confirmation parameters
	foreach (i, PT; PARAMS) {
		static if (isNullable!PT)
			alias ParamBaseType = typeof(PT.init.get());
		else alias ParamBaseType = PT;

		static if (isInstanceOf!(Confirm, ParamBaseType)) {
			enum pidx = param_names.countUntil(PT.confirmedParameter);
			static assert(pidx >= 0, "Unknown confirmation parameter reference \""~PT.confirmedParameter~"\".");
			static assert(pidx != i, "Confirmation parameter \""~PT.confirmedParameter~"\" may not reference itself.");

			bool matched;
			static if (isNullable!PT && isNullable!(PARAMS[pidx])) {
				matched = (params[pidx].isNull() && params[i].isNull()) ||
					(!params[pidx].isNull() && !params[i].isNull() && params[pidx] == params[i]);
			} else {
				static assert(!isNullable!PT && !isNullable!(PARAMS[pidx]),
					"Either both or none of the confirmation and original fields must be nullable.");
				matched = params[pidx] == params[i];
			}

			if (!matched) {
				auto ex = new Exception("Comfirmation field mismatch.");
				static if (erruda.found && ERROR.length == 0) {
					auto err = erruda.value.getError(ex, param_names[i]);
					handleRequest!(erruda.value.displayMethodName, erruda.value.displayMethod)(req, res, instance, settings, err);
					return;
				} else {
					throw new HTTPStatusException(HTTPStatus.badRequest, ex.msg);
				}
			}
		}
	}

	static if (hasAuth)
		handleAuthorization!(C, overload, params)(auth_info);

	// execute the method and write the result
	try {
		import vibe.internal.meta.funcattr;

		static if (staticIndexOf!(WebSocket, PARAMS) >= 0) {
			static assert(is(RET == void), "WebSocket handlers must return void.");
			handleWebSocket((scope ws) {
				foreach (i, PT; PARAMS)
					static if (is(PT == WebSocket))
						params[i] = ws;

				__traits(getMember, instance, M)(params);
			}, req, res);
		} else static if (is(RET == void)) {
			__traits(getMember, instance, M)(params);
		} else {
			auto ret = __traits(getMember, instance, M)(params);
			ret = evaluateOutputModifiers!overload(ret, req, res);

			static if (is(RET : Json)) {
				res.writeJsonBody(ret);
			} else static if (is(RET : InputStream) || is(RET : const ubyte[])) {
				enum type = findFirstUDA!(ContentTypeAttribute, overload);
				static if (type.found) {
					res.writeBody(ret, type.value);
				} else {
					res.writeBody(ret);
				}
			} else static if (is(RET : const(char)[])) {
				res.writeBody(ret);
			} else {
				static assert(is(RET == void), M~": Only `InputStream`, `const(ubyte[])`, `Json`, `const(char)[]` and `void` are supported as return types for route methods.");
			}
		}
	} catch (Exception ex) {
		import vibe.core.log;
		logDebug("Web handler %s has thrown: %s", M, ex);
		static if (erruda.found && ERROR.length == 0) {
			auto err = erruda.value.getError(ex, null);
			handleRequest!(erruda.value.displayMethodName, erruda.value.displayMethod)(req, res, instance, settings, err);
		} else throw ex;
	}
}

private RequestContext createRequestContext(alias handler)(HTTPServerRequest req, HTTPServerResponse res)
{
	RequestContext ret;
	ret.req = req;
	ret.res = res;
	ret.language = determineLanguage!handler(req);

	import vibe.web.i18n;
	import vibe.internal.meta.uda : findFirstUDA;

	alias PARENT = typeof(__traits(parent, handler).init);
	enum FUNCTRANS = findFirstUDA!(TranslationContextAttribute, handler);
	enum PARENTTRANS = findFirstUDA!(TranslationContextAttribute, PARENT);
	static if (FUNCTRANS.found) alias TranslateContext = FUNCTRANS.value.Context;
	else static if (PARENTTRANS.found) alias TranslateContext = PARENTTRANS.value.Context;

	static if (is(TranslateContext) && languageSeq!TranslateContext.length) {
		switch (ret.language) {
			default:
			mixin({
				string ret;
				foreach (lang; TranslateContext.languages) {
					ret ~= "case `" ~ lang ~ "`:
						ret.tr = &tr!(TranslateContext, `" ~ lang ~ "`);
						ret.tr_plural = &tr!(TranslateContext, `" ~ lang ~ "`);
						break;";
				}
				return ret;
			}());
		}
	} else {
		ret.tr = (t,c) => t;
		// Without more knowledge about the requested language, the best we can do is return the msgid as a hint
		// that either a po file is needed for the language, or that a translation entry does not exist for the msgid.
		ret.tr_plural = (txt,ptxt,cnt,ctx) => !ptxt.length || cnt == 1 ? txt : ptxt;
	}

	return ret;
}
